/*
        * Copyright 1995-2000 Sun Microsystems, Inc.  All Rights Reserved.
        * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
        *
        * This code is free software; you can redistribute it and/or modify it
        * under the terms of the GNU General Public License version 2 only, as
        * published by the Free Software Foundation.  Sun designates this
        * particular file as subject to the "Classpath" exception as provided
        * by Sun in the LICENSE file that accompanied this code.
       *
       * This code is distributed in the hope that it will be useful, but WITHOUT
       * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
       * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
       * version 2 for more details (a copy is included in the LICENSE file that
       * accompanied this code).
       *
       * You should have received a copy of the GNU General Public License version
       * 2 along with this work; if not, write to the Free Software Foundation,
       * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
       *
       * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
       * CA 95054 USA or visit www.sun.com if you need additional information or
       * have any questions.
       */
      
      import java.io.OutputStream;
      import java.io.PushbackInputStream;
      import java.io.PrintStream;
      
      /**
       * This class implements a BASE64 Character decoder as specified in RFC1521.
       *
       * This RFC is part of the MIME specification which is published by the
       * Internet Engineering Task Force (IETF). Unlike some other encoding
       * schemes there is nothing in this encoding that tells the decoder
       * where a buffer starts or stops, so to use it you will need to isolate
       * your encoded data into a single chunk and then feed them this decoder.
       * The simplest way to do that is to read all of the encoded data into a
       * string and then use:
       * <pre>
       *      byte    mydata[];
       *      BASE64Decoder base64 = new BASE64Decoder();
       *
       *      mydata = base64.decodeBuffer(bufferString);
       * </pre>
       * This will decode the String in <i>bufferString</i> and give you an array
       * of bytes in the array <i>myData</i>.
       *
       * On errors, this class throws a CEFormatException with the following detail
       * strings:
       * <pre>
       *    "BASE64Decoder: Not enough bytes for an atom."
       * </pre>
       *
       * @author      Chuck McManis
       * @see         CharacterEncoder
       * @see         BASE64Decoder
       */
      
      public class BASE64Decoder {
      
          /** This class has 4 bytes per atom */
          protected int bytesPerAtom() {
              return (4);
          }
     
          /** Any multiple of 4 will do, 72 might be common */
          protected int bytesPerLine() {
              return (72);
          }
      
          /**
          * This character array provides the character to value map
           * based on RFC1521.
           */
          private final static char pem_array[] = {
              //       0   1   2   3   4   5   6   7
                      'A','B','C','D','E','F','G','H', // 0
                      'I','J','K','L','M','N','O','P', // 1
                      'Q','R','S','T','U','V','W','X', // 2
                      'Y','Z','a','b','c','d','e','f', // 3
                      'g','h','i','j','k','l','m','n', // 4
                      'o','p','q','r','s','t','u','v', // 5
                      'w','x','y','z','0','1','2','3', // 6
                      '4','5','6','7','8','9','+','/'  // 7
              };
      
         private final static byte pem_convert_array[] = new byte[256];
      
          static {
              for (int i = 0; i < 255; i++) {
                  pem_convert_array[i] = -1;
              }
              for (int i = 0; i < pem_array.length; i++) {
                  pem_convert_array[pem_array[i]] = (byte) i;
              }
          }
      
         byte decode_buffer[] = new byte[4];
     
         /**
          * Decode one BASE64 atom into 1, 2, or 3 bytes of data.
          */
         protected void decodeAtom(PushbackInputStream inStream, OutputStream outStream, int rem)
             throws java.io.IOException
         {
             int     i;
             byte    a = -1, b = -1, c = -1, d = -1;
     
             if (rem < 2) {
                 throw new CEFormatException("BASE64Decoder: Not enough bytes for an atom.");
             }
             do {
                 i = inStream.read();
                 if (i == -1) {
                     throw new CEStreamExhausted();
                 }
             } while (i == '\n' || i == '\r');
             decode_buffer[0] = (byte) i;
     
             i = readFully(inStream, decode_buffer, 1, rem-1);
             if (i == -1) {
                 throw new CEStreamExhausted();
             }
     
             if (rem > 3 && decode_buffer[3] == '=') {
                 rem = 3;
             }
             if (rem > 2 && decode_buffer[2] == '=') {
                 rem = 2;
             }
             switch (rem) {
             case 4:
                 d = pem_convert_array[decode_buffer[3] & 0xff];
                 // NOBREAK
             case 3:
                 c = pem_convert_array[decode_buffer[2] & 0xff];
                 // NOBREAK
             case 2:
                 b = pem_convert_array[decode_buffer[1] & 0xff];
                 a = pem_convert_array[decode_buffer[0] & 0xff];
                 break;
             }
     
             switch (rem) {
             case 2:
                 outStream.write( (byte)(((a << 2) & 0xfc) | ((b >>> 4) & 3)) );
                 break;
             case 3:
                 outStream.write( (byte) (((a << 2) & 0xfc) | ((b >>> 4) & 3)) );
                 outStream.write( (byte) (((b << 4) & 0xf0) | ((c >>> 2) & 0xf)) );
                 break;
             case 4:
                 outStream.write( (byte) (((a << 2) & 0xfc) | ((b >>> 4) & 3)) );
                 outStream.write( (byte) (((b << 4) & 0xf0) | ((c >>> 2) & 0xf)) );
                 outStream.write( (byte) (((c << 6) & 0xc0) | (d  & 0x3f)) );
                 break;
             }
             return;
         }
     }

